Laser sensitometers are used to generate a series of controlled exposures on a sample of light sensitive material so as to produce exposure patches representative of the sensitivity of such light sensitive material. Typically, these exposure patches are used to measure the response of photographic materials as a function of radiant density.
U.S. Pat. No. 3,677,653, which issued to Hocker, et al on Jul. 14, 1972, discloses a method of exposing photographic material to produce exposure patches. Towards this end the disclosed method in the '653 patent uses a combination of a laser and a negative lens system.
U.S. Pat. No. 5,053,619, which issued to Arimto on Oct. 7, 1991, discloses a variable density scanning apparatus, which includes a semiconductor laser, a dynamic diffraction grating, and a rotating polygonal mirror. The apparatus produces an appropriate exposure as a series of individual dot exposures, also known as a raster scan. A drive circuit is used to change the dot density of the individual exposures.
These patents both suffer from certain limitations. In U.S. Pat. No. 3,677,653, uniform exposures are extremely difficult to produce. Also, the use of a diverging lens in the optical system limits the overall power delivered to the exposure plane.
The U.S. Pat. No. 5,053,619 overcomes the problem of uniform exposure and high density by employing raster scan technology. However, the overlap of dots inherent to raster scan technology produces a complex exposure pattern on the test sample, which causes exposure patterns to have a number of undesirable effects caused by intennittency of the material. Consequently, the subject matter of this patent cannot be used to measure intermittency and reciprocity failure effects on the sample.
A further limitation of both of these systems is that a change in the exposure wavelength requires replacement of the laser system.